Cutting tools which are used for example for metal-removing metal-machining as a rule consist of a base (substrate) of hard metal carbide, cermet, steel or high-speed steel with a wear-resistant single-layer or multi-layer coating of hard metallic substances, oxide layers and the like. Such coatings are applied using CVD (chemical vapour deposition) processes and/or PVD (physical vapour deposition) processes.
From EP 1 253 215 it is known for a multi-layer coating with a base layer of TiAlN and a functional layer of aluminium oxide or aluminium-chromium oxide to be deposited on a hard metal carbide substrate using the PVD process. Here, aluminium oxide is deposited with the single magnetron process during which gamma aluminium oxide is produced predominantly. Aluminium-chromium oxide is deposited using the arc PVD process, producing stable alpha aluminium-chromium oxide, but this has poor bonding to the underlying TiAlN base layer, and depending on the process large numbers of macro particles, so-called droplets, are formed which severely impair the quality of the functional layer.
DE 10 2010 028 558 describes a hybrid PVD process for depositing aluminium-chromium oxide mixed crystal layers in which the cathode atomisation and arc evaporation PVD processes are used simultaneously. Aluminium-chromium oxide mixed crystal layers are obtained predominantly in the stable alpha phase, which are essentially free of macro particles (droplets).
According to the known processes representing the state of the art, it is possible to produce aluminium oxide, aluminium-chromium mixed oxide or mixed oxides with further alloying elements in the stable alpha modification. However, these layers are characterised by poor bonding to the underlying substrate, for example a nitridic base layer, such as a TiAlN layer. The provision of such a base layer is desirable because oxide layers deposited directly onto the surface of the substrate are frequently too brittle to function as a wear prevention layer.